Australia found itself at 4 for 98 with South Africa's pacemen beginning to take charge, until Smith joined Marsh in the middle for an unbeaten 199-run partnership.

Marsh, brought in to replace the injured Shane Watson having only arrived in the Republic on Sunday, hit 12 boundaries on his way to his second Test century.

The number three batsmen, who has struggled with injury problems and poor form over the past year, was seen as a real gamble by selectors, and nearly failed when on 12 he offered a difficult catch to Hashim Amla, who grassed the chance.

South African captain Graeme Smith said at the toss that he wanted to put Australia under pressure at the start of the series, but admitted he was uncertain over the wisdom of putting Australia in to bat.

The pitch was well-grassed and there was early life but conditions eased under a hot sun as the ball lost its shine and Marsh and Smith tamed South Africa's pace-based attack.

Marsh batted with discipline, resisting any risky strokes outside the off stump, and took 118 balls to reach his half-century, with seven fours.

He batted particularly impressively after South Africa took the second new ball late in the day.

"He was amazing all day, he let the ball come into his areas and then capitalised on it,'' batting partner Steve Smith said.

"It took the rest of us a week to get over the jet lag, so it must have been hard for him being here only three days."

After overcoming early pressure Smith said the Australians must go on with the job and post a big first-innings score.

"We knew it would be tough initially but it has turned into a good wicket and there are now a couple of cracks developing," he said.

"We will want to get a big first-innings total and then hope the cracks begin to play a part in the game."

Smith also clobbered 12 boundaries and will be eager to get amongst the runs on day two in the hunt for a fourth Test ton, following on from his excellent Ashes form with the bat.

David Warner (12) was the first to fall on day one, chopping Dale Steyn onto his stumps, before Chris Rogers (4) edged Morne Morkel to JP Duminy at silly mid-on.

Alex Doolan made his Test debut for Australia and looked good early on, hitting five boundaries in a confident knock.

But Doolan was eventually out for 27 thanks to a good Robin Peterson catch at mid-wicket off Ryan McLaren's bowling.

Captain Michael Clarke (23) looked to engineer a recovery himself, coming to the crease at 3 for 72, but he fell just short of the team's 100 mark as he top-edged Steyn to Vernon Philander at fine-leg.

But Marsh and Smith proceeded to give a clinic in patient play, punishing bad balls as they came and picking up regular singles.